In exploration and extraction of hydrocarbons, such as fossil fuels (e.g. oil) and natural gas, from underground wellbores extending deeply below the surface, various downhole tools are inserted below the ground surface and include sometimes complex machinery and explosive devices. Examples of the types of equipment useful in exploration and extraction, in particular for oil well drilling applications, include logging tools and perforation gun systems and assemblies. It is often useful to be able to maintain a pressure across one or more components as necessary to ensure that fluid does not leak into the gun assembly, for instance. It is not uncommon that components such as an initiator are components in such perforating gun assemblies that succumb to pressure leakage. It is particularly useful that one or more of the components is able to maintain a pressure differential even after, for instance, detonation of one or more downstream components.
The initiator is one of many components of the perforating gun system for which continual improvement is sought. There are at least 2 known types of initiators—a detonator and an igniter.
Upon placement into the perforating gun assembly, one or more initiators have traditionally required physical connection of electrical wires. The electrical wires typically travel from the surface down to the perforating gun assembly, and are responsible for passing along the surface signal required to initiate ignition. The surface signal typically travels from the surface along the electrical wires that run from the surface to one or more detonators positioned within the perforating gun assembly. Such initiators typically require electronic componentry and/or wiring to pass through a body thereof, (e.g. electric feed-through), and a need exists to provide such componentry having electric feed-through while maintaining a differential pressure across the component. Passage of such wires through the initiator, while maintaining a pressure differential across the component, has proved challenging.
Assembly of a perforating gun requires assembly of multiple parts, which typically include at least the following components: a housing or outer gun barrel within which is positioned an electrical wire for communicating from the surface to initiate ignition, an initiator, a detonating cord, one or more charges which are held in an inner tube, strip or carrying device and, where necessary, one or more boosters. Assembly typically includes threaded insertion of one component into another by screwing or twisting the components into place, optionally by use of a tandem adapter. Since the electrical wire must extend through much of the perforating gun assembly, it is easily twisted and crimped during assembly. In addition, when a wired detonator is used it must be manually connected to the electrical wire, which has lead to multiple problems. Due to the rotating assembly of parts, the wires can become torn, twisted and/or crimped/nicked, the wires may be inadvertently disconnected, or even mis-connected in error during assembly, not to mention the safety issues associated with physically and manually wiring live explosives.
According to the prior art and as shown in FIG. 1, a wired detonator 60 has been configured such that wires must be physically, manually connected upon configuration of the perforating gun assembly. As shown herein, the wired detonator 60 typically has two (or more) wires, which require manual, physical connection once the wired detonator is placed into the perforating gun assembly. (It is possible to have one or more wires whereby one wire could also be a contact as described in greater detail below and as found, for instance, in a spring-contact detonator, commercially available from DynaEnergetics GmbH & Co. KG without the benefit of selectivity and whereby a second connection would be through a shell or head of the detonator.) For detonators with a wired integrated switch for selective perforating, the wires include at least a signal-in wire 61, a signal-out wire 62 and a ground wire 63, while it is possible that only two wires are provided and the third or ground connection is made by connecting the third wire to the shell or head of the detonator. In a typical manual, physical connection, the wires extending along the perforating gun are matched to the wires of the detonator, and an inner metallic portion of one wire is twisted together with an inner metallic portion of the matched wire using an electrical connector cap or wire nut or a scotch-lock type connector. Although not shown, maintenance of the pressure differential across such devices has occurred (minimally) via usage of rubber components including o-rings, rubber stoppers and the like.
Improvements to the way these electrical connections are accomplished include connections and arrangements as found in commonly assigned patent applications PCT/EP2012/056609 (in which an initiator head is adapted to easily introduce external wires into the plug without having to strip the wires of insulation beforehand) and DE 10 2013 109 227.6 (in which a wireless initiator is provided), which are incorporated herein by reference in their entirety.
The assembly described herein further solves the problems associated with prior known assemblies in that it provides, in an embodiment, an assembly to improve manufacturing costs and assembly in the field, as described in greater detail hereinbelow.